FCM Notification Scheduler Development

The react native expo app at the moment is rescheduling only when app opens but not in background or closed state.

I need a reliable server-side script or REST API to schedule and send Firebase Cloud Messaging (FCM) notifications at specific times, even when my React Native Expo app is in the background or terminated state.

Key Requirements:
- Develop a lightweight scheduler on my Ubuntu server.
- Trigger FCM alerts through Firebase’s API.
- Manage notifications via config files or an admin endpoint (flexible based on preference).
- Ensure the solution is robust and easy to maintain.

Ideal Skills and Experience:
- Hands-on experience in React Native.
- Proficient in Ubuntu server environments.
- Strong background in Firebase integration.
- Experience in developing REST APIs and server-side scripts.